#include<stdio.h>

double CancelFee(double price);
int main(void)
{
	double input;
	
	scanf("%lf",&input);
	printf("%.1lf",CancelFee(input));
	
	return 0;
}
double CancelFee(double price)
{
	int price_int;
	double price_double;
	
	price*=0.05;
	price_int=(int)price;
	price_double=price-price_int;
	
	if(price_double<0.25)
	{
		return (double)price_int;
	}
	else if(price_double>=0.25&&price_double<0.75)
	{
		return (double)price_int+0.5;
	}
	else
	{
		return (double)(price_int+1);
	}
}
